Hi Jon,
Micro-stepping is a property of the motor amplifier (motor drive) rather than the controller. It sounds like you are using a 3rd party drive, since you have a UMI. You want to check with your motor amplifier documentation to see if it's supported. Usually, there will be dip-switches on the drive that sets the microstep factor.
Hope this helps. Please let me know if you have any questions.
Thanks,
Ken Sun
Applications Engineering
National Instruments